Constraints on Radon and SGD Temporal Variability in a Semiarid, Well Mixed Estuary
Abstract
Submarine groundwater discharge (SGD) is defined as any and all types of water flow from the seabed to the coastal ocean, which includes both terrestrial/groundwater and oceanic/recirculated components. Although diffuse, and difficult to measure, SGD represents a significant source of freshwater and solutes to near-shore marine environments. Because radioisotopes like 222Rn (t1/2 = 3.82 days) and its parent, 226Ra (t1/2 1600 years), are more concentrated in groundwater than surface waters, they are ideal tracers of SGD in marine environments. Here we measure surface water variability of tracer activity in response to atmospheric and hydrologic factors. This multi-seasonal study measures 222Rn nearly continuously at a near-shore platform every 30 minutes since Summer of 2019, while 226Ra is measured 1-3 times per week at the same site. Hydroparameters at the study site (wind speed, wind direction, groundwater and tide level, temperature, salinity and precipitation) are recorded simultaneously and correlated to tracer measurements. Initial results reveal trends that would otherwise be obscured over shorter study periods. Wind direction and speed appear to be largely responsible for the observed radon variability. Additionally, tide and groundwater levels appear to be correlated to radon levels, often compounding or obscuring the wind effect. Long-term observations allow for multi-linear regression and generalized additive modeling, providing numerical relationships between environmental factors and tracer behavior. The resulting correlations will be integrated into a radon mass-balance for SGD estimates that accounts for atmospheric controls on tracer activity, reducing uncertainties associated with a traditional mass-balance approach. Additionally, these observations will be used to create a prediction model for radon in surface water to better understand seasonal trends.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMH033.0006W
- Keywords:
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- 1830 Groundwater/surface water interaction;
- HYDROLOGY;
- 4306 Multihazards;
- NATURAL HAZARDS;
- 4217 Coastal processes;
- OCEANOGRAPHY: GENERAL;
- 4235 Estuarine processes;
- OCEANOGRAPHY: GENERAL